In recent years, X-ray Computed Tomography (CT) apparatuses are configured to be able to obtain tomography images having a high level of precision by varying X-ray radiation angles with fine granularity and by introducing an X-ray detector in which X-ray detecting elements are arranged with a high density. Due to the endeavor to obtain tomography images having a high level of precision, the resolution of X-ray projection data becomes higher, the number of images taken per time period increases, and the costs of data storage and data transfer thus become higher. For this reason, X-ray CT apparatuses are configured to suppress the data increase by compressing data related to medical images, such as X-ray detection data.
Further, X-ray CT apparatuses have been developed to adopt a multi-slice system and to achieve a higher speed. To realize the multi-slice system and to achieve a higher speed, it is necessary to process a large amount of data in a real-time manner. To compress the large amount of data in a real-time manner, it is necessary to divide the data into a plurality of pieces and to compress the pieces of data in a parallel manner.
However, when data related to a medical image is divided into pieces and compressed in such a manner that the medical image is divided into two areas, the pixel values may be discontinuous across the boundary of the division. Thus, there is a possibility that the image quality may be found degraded when the pieces of data compressed in parallel are combined together and reconstructed.